Implantable medical devices use electrical power to operate and provide therapies which can include monitoring and stimulation. When therapy is provided or adjusted programmably, using an external patient controller, communication between the external and internal components of the medical system also requires power. An implantable device can monitor the heart and alert the patient when an abnormal cardiac state occurs so that they may seek intervention such as is described in U.S. Pat. No. 6,609,023 and US20070016089, both to Fischell et al. The implantable device may also use this monitoring in delivering responsive therapy such as pacing the heart, delivering a drug, or stimulating nerve tissue of the brain or body as described in U.S. Pat. No. 6,066,163, to John.
An implantable medical device can be a neurostimulation device which performs sensing and/or modulation of neural activity in the treatment of, for example, epilepsy, motor, pain, psychiatric, mood, degenerative, and aged-related disorders. Neurostimulators can be located in the brain, in the skull, or in the body. This last embodiment will require that electrode leads transverse the neck so that they can stimulate their intended neural targets within the brain. Vagal and cranial nerve stimulators may also be used for therapies related to modulation of the brain or body (as may occur directly or by way of an intervening neural target). Implantable medical devices may be placed throughout the body to modulate the activity of different organs and biological processes, and include devices used in the provision of therapy for eating disorders, pain, migraine, and metabolic disorders such as diabetes. As the duration of sensing, processing, monitoring, and stimulation increases the amount of power needed will also increase.
The reliability and longevity of a power source is major issue in operating implantable medical devices. Numerous advances have addressed power requirements including improvements in materials, (re-)charging methods, and technologies. Incorporation of dual battery paradigms has also provided benefits since the two batteries can differ in characteristics of energy storage, chemistry and power output capacities, in order to, for example, reach a compromise between high-energy output and sustainability. Implantable devices themselves have also been improved with features such as “sleep” and “low power” modes, where less energy is needed. Regardless of these improvements, all device operations require power, including monitoring, processing of monitored data, stimulation, and communication with external devices.
A top reason for surgical removal of neurostimulators and other types of implanted devices is longevity of the power source. The need for surgical removal of an entire implanted device traditionally occurs because the battery is integrated into the device itself. This design-related issue can be addressed somewhat by having a separate skull-mounted power module which resides adjacent to the neuronal-stimulator. However, surgery for selective removal/replacement of the power source is still invasive. Further, aside from issues of replacement, in ongoing use of implanted devices, a more robust supply of power can provide improved therapy.
The current invention can incorporate a number of existing technologies such as U.S. Pat. No. 6,108,579, which discloses a battery-monitoring apparatus and method which includes features of tracking power usage, monitoring battery state, and displaying the estimated remaining life of the battery power source. U.S. Pat. No. 6,067,473 discloses a battery-monitoring apparatus and method which includes features of providing audible warnings of low battery life using both tones and pre-recorded verbal warnings of battery depletion. U.S. Pat. Nos. 5,957,956, 5,697,956, 5,522,856, and US 20050021134 to Opie, and 20050033382 to Single, disclose devices having features such as: relatively small mass and a minimal rate of power consumption; means for optimizing current drain; improved shelf storage capacity; minimizing the power requirements of battery power sources; temperature regulation of the power source; and dual battery implementation including use of back-up battery to avoid power disruption. U.S. Pat. No. 7,127,293 to MacDonald describes a biothermal power source for implantable devices and describes methods and materials which are suitable for use in the current invention.
There is a need to provide an improved power supply means for recharging of a power supply of an implantable medical device. Power supply improvements will allow improvements in the performance of the device. Recharging should not require recharging or replacement of the power source in a manner which is unreliable or which places an undue burden on the patient.
The invention provides improved power harvesting, generation and supply and can rely upon naturally occurring sources of energy for at least a portion of its recharging needs. The invention also provides improved power harvesting of transmitted energy.